1. Field of the Invention
This invention relates to an image-wise exposure apparatus, wherein a photosensitive material is exposed image-wise by use of a mirror array device.
2. Description of the Related Art
As described, for instance, in "O plus E" magazine, the October number, 1994, pp. 90-94, there has been known a mirror array device comprising a plurality of small mirrors which are arranged in the form of a two-dimensional array, and a drive means for changing the orientations of the respective small mirrors independently from each other so that light impinging upon each of the small mirrors is reflected selectively toward one of two directions.
With such a mirror array device, an image can be projected onto a predetermined projection surface via the mirror array device while modulating the light impinging upon the projection surface for each of the small mirrors by controlling the drive means according to an image signal. When a photosensitive material is located on the projection surface, the photosensitive material can be exposed image-wise. (An example of such an image-wise exposure apparatus is disclosed in this applicant's Japanese Patent Application No. 8(1996)-39489)
Further the amount of light impinging upon the photosensitive material can be controlled for each of the small mirrors by, for instance, pulse width modulation of the on time of each small mirror (i.e., the time each smaller mirror is set in the orientation in which the light is caused to impinge upon the photosensitive material) within a frame time, whereby a gradation image can be formed on the photosensitive material.
Generally such a mirror array device is monolithically formed on a substrate (typically of silicone) and each small mirror is arranged to selectively take a position where it is inclined by an angle .theta. with respect to the substrate surface and a position where it is inclined by an angle -.theta. with respect to the substrate surface. When the mirror is in one of the two positions, the recording light impinging upon the mirror is caused to impinge upon the photosensitive material and when the mirror is in the other position, the recording light impinging upon the mirror cannot impinge upon the photosensitive material.
In an image-wise exposure apparatus using such a mirror array device, an image forming lens which causes light from the mirror array device to form an image on the photosensitive material is provided. Conventionally the image forming lens is positioned so that its optical axis is in alignment with the line which is perpendicular to the substrate surface and passes through the center of the mirror array device.
However the conventional image-wise recording apparatus where the image forming lens is positioned in the manner described above is disadvantageous in that the conjugate distance of the optical system becomes too long and the overall size of the apparatus is greatly enlarged in order to prevent interference of the recording light impinging upon the mirror array device and the reflected light from the mirror array device with each other.